This invention relates in general to image forming devices and, more particularly, to pre-heating media in an input tray for reducing media curl caused by image processing.
Conventional electrophotographic imaging devices, such as laser printers, facsimile machines or copiers, operate by using a roller or a series of rollers to pull a sheet of media (typically a sheet of paper) from an input tray and to move the media to a registration roller assembly. The registration roller assembly aligns the media so that the edges of the media are parallel to the media path. Once the media is properly aligned, the registration roller assembly passes the media to an optical photoconductor (OPC) surface, such as a drum or belt. The OPC has a latent image on its surface formed by scanning a laser across the surface. A difference in electrostatic charge density is created between the areas on the surface exposed and unexposed to the laser beam. A visible image is developed by toners that are selectively attracted to the OPC surface, either exposed or unexposed to light, depending on the relative electrostatic charges of the OPC surface, development electrode, and the toner. The OPC may be either positively or negatively charged, and the toner similarly may contain negatively or positively charged particles.
The media is given an electrostatic charge and passed close to the photoconductor surface. As the media passes close to the photoconductor surface, it pulls the toner from the photoconductor surface onto the media still in the pattern of the image developed from the photoconductor surface. After receiving the image, the media is passed to a fuser. The fuser heats the toner image on the media, bonding the toner to the media.
The temperature of the fuser is critical. Rough or thick media requires a higher fuser temperature than smooth or thin media. In either case, if the fuser temperature is too low, toner will not be adequately fused to the media. On the other hand, if the temperature is too high, the toner will be pulled from the media by the fuser and the media may be damaged. Either case results in an undesirable print defect.
Notably, over fusing can cause the media to curl, wrinkle, or warp and possibly jam the printer. However, other factors also affect media curl, wrinkle or warping, including composition and weight of the media, moisture content of the media, whether one or both sides of the media is imaged, toner distribution on the media, fusing temperature, fusing configuration (i.e., single or dual heated fuser rollers), ejection speed of the media when leaving the printer, and external environmental factors such as temperature and humidity. For example, media curl is common in environments where air conditioning is unavailable to moderate humid conditions. In such situations, media moisture content is naturally high. As a result, media curl, wrinkle or warping may occur simply due to the moisture being quickly driven off during normal image fusing, even if the printer parameters are optimally established.
Many of these factors affect media curl not only in electrophotographic imaging systems but also in ink jet imaging systems. For example, notably, the heavy moisture concentrations in conventional liquid inks causes the inks to soak into conventional paper media and, in combination with ink distribution on the media, causes the media to curl, wrinkle or warp.
Accordingly, an object of the present invention is to reduce media curl often caused by conventional image processing techniques and environmental conditions.
According to principles of the present invention, a media input tray for an imaging device such as a laser printer is configured to heat media in the tray in order to reduce potential curl of the media caused by image processing in the imaging device. In a preferred embodiment, the input tray is configured with a flexible printed circuit having conductive traces for dissipating heat in response to an electric current. The flexible circuit is coupled to a power supply in the imaging device to enable a continuous warming of media in the tray, independent of imaging operations by the imaging device.
According to further principles, a method of image processing includes providing a heating device in a media input tray of an image processing device and heating the media disposed in the input tray with the heating device such that potential media curl, caused by image processing operations, is reduced.
Other objects, advantages, and capabilities of the present invention will become more apparent as the description proceeds.